Question 945957
8 men plough 1 field in 9 hrs
1/8 that number of men will take 8 
times as long to plough 1 field
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1 man ploughs 1 field in 72 hrs
18 times as many men will take 1/18
of that time to plough 1 field
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18 men plough 1 field in 72/18 = 4 hrs
The answer is (d)